Conditional CSS for FF, IE7, IE6

Set different values for an element based on browser (specifically, how the browser interprets the CSS). Definitions must be in order as shown below because newer definitions override existing.

The first setting will apply to all browsers.
The second setting (using a pound symbol, #) will only apply to Microsoft Internet Explorer.
The third setting (an underscore, _ ) will only apply to IE browsers 6.0 and older.